A technology for sensing presence or absence of a person in an illuminated space (a region of a captured image) based on an image sensor with a solid-state image sensing device such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) has been known so far. There is proposed a lighting system that applies such a technology to lighting control and is configured to turn on a lighting fixture (a lighting load) when it is judged that a person is present in an illuminated space, based on a captured image by an image sensor. Such a lighting (control) system is described in JP Pub. No. 2011-113767 (hereinafter referred to as “Document 1”).
A lighting control device used for the lighting system described in Document 1 has a function for alternately switching between a first mode for sensing presence or absence of a person in an illuminated space based on the image sensor and a second mode for detecting brightness of the illuminated space based on the image sensor. The lighting control device is configured to control a lighting fixture so that in the first mode, a lighting state of the lighting fixture is changed if the presence of the person in the illuminated space is sensed from a captured image, and so that in the second mode, an average value of brightness values of the captured image is included in a target range.
When detecting the brightness, the lighting control device also uses, for calculation of the average value of brightness values, only brightness values in a pixel range(s) of the captured image, which does not include an image of the person. The lighting control device can accordingly calculate the average value of brightness values except for the pixel range(s) of which brightness values have large changes, and enhance precision of brightness control.
The lighting control device described in Document 1 is to perform control such that the average value of brightness values of the captured image corresponding to brightness of the illuminated space approaches a target value regardless of whether or not external light enters the illuminated space. Accordingly, when the control object of the lighting control device is lighting fixtures, it is necessary to light lighting fixtures in not only an area in which a person is present, but also an area in which no person is present, in order to make the brightness of the illuminated space approach the target value in a state of no external light entering the illuminated space. As a result, energy-saving effect by introduction of the lighting system may be reduced.